The <i>Ectocarpus</i> genome and the independent evolution of multicellularity in brown algae

Brown algae (Phaeophyceae) are complex photosynthetic organisms with a very different evolutionary history to green plants, to which they are only distantly related1. These seaweeds are the dominant species in rocky coastal ecosystems and they exhibit many interesting adaptations to these, often harsh, environments. Brown algae are also one of only a small number of eukaryotic lineages that have evolved complex multicellularity (Fig. 1).We report the 214 million base pair (Mbp) genome sequence of the filamentous seaweed Ectocarpus siliculosus (Dillwyn) Lyngbye, a model organism for brown algae, closely related to the kelps (Fig. 1). Genome features such as the presence of an extended set of light-harvesting and pigment biosynthesis genes and new metabolic processes such as halide metabolism help explain the ability of this organism to cope with the highly variable tidal environment. The evolution of multicellularity in this lineage is correlated with the presence of a rich array of signal transduction genes. Of particular interest is the presence of a family of receptor kinases, as the independent evolution of related molecules has been linked with the emergence of multicellularity in both the animal and green plant lineages. The Ectocarpus genome sequence represents an important step towards developing this organism as a model species, providing the possibility to combine genomic and genetic2 approaches to explore these and other aspects of brown algal biology further

Crystal and Molecular Structure of Dihydroxo (5,10,15,20-tetraphenylporphinato) phosphorus(V) Hydroxyde Dihydrate.

The structure of dihydroxo(5,10,15,20-tetraphenylporphinato)phosphorus(V) hydroxide dihydrate, (C4H3,,02P+)(OH-).2H20, has been determined from three-dimensional diffractometer data. It crystallizes in the monoclinic space group P2,/c with a = 14.636 (4) A, b = 13.953 (3) A, c = 17.592 (4) A, /3 = 90.21 (2)", and Z = 4. The structure was solved by heavy-atom methods and refined by full-matrix least-squares methods to yield a final R factor of 0.090. This is the first reported structural analysis of a "metalloporphyrin" where the central ion is a nonmetal. The coordination geometry is distorted octahedral with the phosphorus atom displaced 0.09 8, from the mean plane of the pyrrole nitrogen atoms. The P-N bond lengths range from 1.87 (1) to 1.92 (1) 8,. The two P-O distances are 1.644 (8) and 1.545 (8) 8,. The porphyrin ring shows marked S4 deviations from planarity. There is extensive hydrogen bonding between the axial hydroxyl groups, the hydroxide counterion and the waters of hydration forming quasi-linear hydrogen-bonded polymers

New insights on Laminaria digitata ultrastructure through combined conventional chemical fixation and cryofixation

The objective of the present study is to examine the fine structure of vegetative cells of Laminaria digitata using both chemical fixation and cryofixation. Laminaria digitata was chosen due to its importance as a model organism in a wide range of biological studies, as a keystone species on rocky shores of the North Atlantic, its use of iodide as a unique inorganic antioxidant, and its significance as a raw material for the production of alginate. Details of the fine structural features of vegetative cells are described, with particular emphasis on the differences between the two methods used, i.e. conventional chemical fixation and freeze-fixation. The general structure of the cells was similar to that already described, with minor differences between the different cell types. An intense activity of the Golgi system was found associated with the thick external cell wall, with large dictyosomes from which numerous vesicles and cisternae are released. An interesting type of cisternae was found in the cryofixed material, which was not visible with the chemical fixation. These are elongated structures, in sections appearing tubule-like, close to the external cell wall or to young internal walls. An increased number of these structures was observed near the plasmodesmata of the pit fields. They are similar to the &quot;flat cisternae&quot;found associated with the forming cytokinetic diaphragm of brown algae. Their possible role is discussed. The new findings of this work underline the importance of such combined studies which reveal new data not known until now using the old conventional methods. The main conclusion of the present study is that cryofixation is the method of choice for studying Laminaria cytology by transmission electron microscopy. © 2021 Walter de Gruyter GmbH, Berlin/Boston 2021